impala Union条款
您可以使用Impala的Union子句组合两个查询的结果。
语法
以下是Impala中的Union子句的语法。
query1 union query2;
例
假设我们在数据库my_db中有一个名为customers的表，其内容如下 -
[quickstart.cloudera:21000] > select * from customers; Query: select * from customers +----+----------+-----+-----------+--------+ | id | name | age | address | salary | +----+----------+-----+-----------+--------+ | 1 | Ramesh | 32 | Ahmedabad | 20000 | | 9 | robert | 23 | banglore | 28000 | | 2 | Khilan | 25 | Delhi | 15000 | | 4 | Chaitali | 25 | Mumbai | 35000 | | 7 | ram | 25 | chennai | 23000 | | 6 | Komal | 22 | MP | 32000 | | 8 | ram | 22 | vizag | 31000 | | 5 | Hardik | 27 | Bhopal | 40000 | | 3 | kaushik | 23 | Kota | 30000 | +----+----------+-----+-----------+--------+ Fetched 9 row(s) in 0.59s
同样，假设我们有另一个名为employee的表，其内容如下 -
[quickstart.cloudera:21000] > select * from employee; Query: select * from employee +----+---------+-----+---------+--------+ | id | name | age | address | salary | +----+---------+-----+---------+--------+ | 3 | mahesh | 54 | Chennai | 55000 | | 2 | ramesh | 44 | Chennai | 50000 | | 4 | Rupesh | 64 | Delhi | 60000 | | 1 | subhash | 34 | Delhi | 40000 | +----+---------+-----+---------+--------+ Fetched 4 row(s) in 0.59s
以下是Impala中的union子句的示例。 在此示例中，我们按照ID的顺序在两个表中排列记录，并使用两个单独的查询并使用UNION子句连接这些查询来将其数量限制为3。
[quickstart.cloudera:21000] > select * from customers order by id limit 3 union select * from employee order by id limit 3;
执行时，上述查询给出以下输出。
Query: select * from customers order by id limit 3 union select * from employee order by id limit 3 +----+---------+-----+-----------+--------+ | id | name | age | address | salary | +----+---------+-----+-----------+--------+ | 2 | Khilan | 25 | Delhi | 15000 | | 3 | mahesh | 54 | Chennai | 55000 | | 1 | subhash | 34 | Delhi | 40000 | | 2 | ramesh | 44 | Chennai | 50000 | | 3 | kaushik | 23 | Kota | 30000 | | 1 | Ramesh | 32 | Ahmedabad | 20000 | +----+---------+-----+-----------+--------+ Fetched 6 row(s) in 3.11s
